Thanks to @pfalcon for the tip!

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.

Convert unix open() to such.

Some tools do not support local/static symbols (one example is GNU ld map file).
Exposing all functions will allow to do detailed size comparisons, etc.

Also, added bunch of statics where they were missing, and replaced few identity
functions with global mp_identity().

Please don't submit patches with tab indentation!

Test function needs to be called by something else. Test heap size reduced so
its dump fits on a screenful of a typical terminal.

With a nice traceback, helps debugging much better.

If there's malloc and memset, then there's no need for calloc, especially if
we need to implement it ourselves.

Unlike CPython socket, microsocket object already implements stream protocol
(read/write methods), so makefile() just returns object itself. TODO: this
doesn't take care of arguments CPython's makefile() may accept.

Passing keyword arguments to a native function now no longer requires
heap memory.  The kw_args map is created on the stack using the args
array as the table.

This allows keyword maps to be created directly from stack data.

Can't decide which is better for string type, char or byte pointer.
Changing to char removes a few casts.  Really need to do proper unicode.